1. Field of the Invention
The present invention relates generally to systems and methods for measuring hole bore properties, and specifically to a method and apparatus for measuring the bore diameter of as a function of hole depth.
2. Description of the Related Art
Hundreds of thousands of holes are drilled in commercial and military aircraft and spacecraft. Some of these holes are high tolerance holes with a diameter tolerance band of 0.003 inch. Specifications dictate the measurement requirements of these holes, and they typically mandate the measurement of the maximum and minimum diameter at two orientations in the bore of the hole.
Inspectors currently utilize available hole diameter gages that only report a single diameter in the bore of the hole at an uncontrolled and unmeasured depth in the bore. Currently, inspectors are required to insert the gage into the hole and hunt for the minimum and maximum hole diameter readings. The effort challenges the user since the reading ability of the user is slow compared to the rate of change in hole's bore diameter. Using current techniques, it can take approximately ninety seconds to measure the bore of a single hole, and the results can greatly depend on the skill of the inspector.
Since controlling the rate of descent into the hole is challenging, the true maximum and minimum hole diameters are often missed. Hole diameter specifications also typically dictate that the hole readings be taken within a specific depth distance to the entrance and exit of the hole. Further, part interfaces are typically ignored since these areas do not represent the true drilling process. Without a depth reference, it is not possible to exactly judge what depth the gage is at and hence the specified setback requirements cannot be properly met.
What is needed is a method and apparatus for determining the bore diameter of a hole as a function of the depth of the hole. The present invention satisfies that need.